This invention relates to crystallizable thermoplastic butene-1 polymers. More particularly, this invention is directed to the addition of a small amount of substantially graphitic non-turbostratic carbon to a butene-1 polymer, which affords compositions which crystallize from the melt at a faster rate and exhibit improved properties, compared to the non-nucleated butene-1 base polymer.
Heterogeneous nucleation via the addition of a foreign material or nucleating agent, which promotes crystallization of the polymers from the melt, is well known. See, for example, Chatterjee et al, J. Polym. Sci.; Polym. Phys. Ed., Vol. 13, 2369-83 and 2385-90 (1975). As demonstrated therein, heterogeneous nucleation is highly selective and there is no evidence of a universally strong nucleating agent for all polymers. In other words, an effective nucleating agent for one polymer may be ineffective for even a closely related polymer; similarly, even a compound closely related to an effective nucleating agent for one polymer may be ineffective for that same polymer.
The use of a nucleating agent to accelerate crystallization allows for faster processing and results in a more uniform microstructure because of the reduced size of the spherulites which form upon melt crystallization. The products also generally demonstrate improved physical and mechanical properties. See, for example, Rubin, Injection Molding Theory and Practice, pp. 192ff (1972). In general, a desirable nucleating agent is effective at low levels of addition, both for reasons of economy and the avoidance of undue foreign structural heterogeneity which may otherwise affect the properties of the polymer. It has now been discovered that substantially graphitic non-turbostratic carbon is a highly effective nucleating agent, even at low levels of addition, for butene-1 homopolymers and copolymers with ethylene. Carbon black, an amorphous turbostratic carbon, is much less effective for nucleation of butene-1 polymers than the substantially graphitic carbon of this invention.
The row nucleation of isotactic polypropylene on graphite fibers is disclosed in Hobbs, Nature Physical Science, Vol. 234, No. 44, p. 12ff (Nov. 1, 1971). The graphite used is described as having a turbostratic structure and no experiments with butene-1 polymers were performed.
U.S. Pat. No. 3,902,532 discloses pipe formed from poly(1-monoolefin) compositions containing small amounts of graphite and optionally carbon black. The patent is directed mainly to ethylene polymers and no specific form of graphite is required. The graphite is used in amounts higher than have now been discovered as effective for nucleation, and is added to produce pipe with high hoop-stress life.
Belgian Pat. No. 695,803 and British Pat. No. 1,328,444 disclose a variety of nucleating agents for butene-1 polymers. Specific examples include polypropylene, coumarone-indene resin, aluminum silicate, clay and aromatic sulfonic acids.